/// <summary>
/// Generates a full key pair (Public and private) given the private key
/// </summary>
/// <param name="privateKey">The private key to generate public key from</param>
/// <returns>A full key pair</returns>
public static X25519KeyPair GenerateKeyFromPrivateKey(byte[] privateKey)
{
X25519KeyPair key = new X25519KeyPair
{
PrivateKey = privateKey
};
key.PublicKey = Curve25519.ScalarMultiplication(key.PrivateKey, Curve25519.Basepoint);
return(key);
}
/// <summary>
/// Uses RNG Random to generate a key pair
/// </summary>
/// <returns>A random key pair</returns>
public static X25519KeyPair GenerateKeyPair()
{
// at first generate the private key
X25519KeyPair key = new X25519KeyPair
{
PrivateKey = new byte[32]
};
using (var rnd = new RNGCryptoServiceProvider())
rnd.GetBytes(key.PrivateKey);
// as defined in https://cr.yp.to/ecdh.html do these operation to finalize the private key
key.PrivateKey[0] &= 248;
key.PrivateKey[31] &= 127;
key.PrivateKey[31] |= 64;
// compute the public key
key.PublicKey = Curve25519.ScalarMultiplication(key.PrivateKey, Curve25519.Basepoint);
return(key);
}
/// <summary>
/// Generate a shared secret with the other users public key and your private key
/// </summary>
/// <param name="myPrivateKey">Your private key</param>
/// <param name="otherPublicKey">The public key of the other user</param>
/// <returns>A shared secret</returns>
public static byte[] Agreement(byte[] myPrivateKey, byte[] otherPublicKey)
{
return(Curve25519.ScalarMultiplication(myPrivateKey, otherPublicKey));
}